The ability to transmit many diverse forms of information (e.g. voice, video, image, graphics, text, computer data, control data, electronic funds, electronic mail, etc.) in an integrated manner, across a general purpose communications network, has long been a requirement. The existing current problem is that most forms of information transfer may be clearly classified into two distinct and mutually opposing categories depending upon the requirements they impose upon the communications network. Signals such as voice and video present a reasonably constant traffic load to the network and can tolerate a relatively high loss and error rate within the network, but exhibit critical delay and delay variance requirements. At the other end of the spectrum the vast majority of examples of data transfer present a highly and rapidly fluctuating traffic demand and are extremely intolerant to errors in transmission, but can tolerate a high and variable delay. Due to the opposing nature of these two classes of traffic, two very different methods of switching have been developed to support their electronic communication; circuit switching and packet switching. Though many attempts have been made, so far these two switching mechanisms have proved very difficult to integrate into a single communications network of commercial significance.
It is an aim of this invention firstly to provide a self-routing switching element for use in a high capacity, fast packet switch operating according to the technique of asynchronous time division, and also to provide such an asynchronous time switch enabled by the incorporation of said switching elements, which has the capability for handling both voice and data traffic by virtue of the use of packet switching, with very small packets, in combination with virtual circuits across the network.